A processor core may include one or more execution units (EUs) able to execute micro-operations (“u-ops”), for example, utilizing an out-of-order (OOO) subsystem. For example, an instruction decoder (ID) may decode a macro-instruction, intended for execution by the processor, into micro-operations. A reservation station (RS) may dispatch the micro-operations to the EUs for execution.
The RS may utilize speculative write-back indications, for example, to allow processing of relatively “young” micro-operations, e.g., even if processing of a currently-executed micro-operation may not compete successfully. Write-back indications may be sent, for example, by the RS to a register-alias table (RAT) which may perform register renaming, e.g., logical to physical mapping of registers. Based on the assumption that no invalid data exists, other micro-operations may be considered for scheduling for execution in parallel to reading sources from a register file.
Unfortunately, a write-back indication may turn out to be incorrect, and a performance penalty may be required to avoid processing of invalid data. For example, the RAT may track availability of data on a reorder buffer (ROB) entry; if a write-back indication is not followed by valid data, then the RAT may indicate that the result of the micro-operation is available in the ROB, thereby allowing allocation of ROB read ports. However, the RS may not be able to immediately consider for scheduling the next micro-operation for execution, since the speculative write-back indication may be incorrect. Instead, a “valid” bit may be read from the ROB and sent to the RS, thereby resulting in a performance delay of one or more processing cycles.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.